1. Field of the Invention
The present invention relates to a backlight unit for a liquid crystal display using a light emitting diode and a manufacturing method thereof, and more particularly, a backlight unit which is significantly decreased in the number of parts such as printed circuit boards (PCBs), connectors for connecting the PCBs having light emitting diodes mounted thereon and structures for fixing the PCBs, and simplified in manufacturing and assembling processes, and a manufacturing method thereof.
2. Description of the Related Art
With a recent trend of greater thinness and higher performance of display devices, liquid displays are widely utilized in TVs and monitors. The liquid display panel does not emit light on its own, thus requiring an additional backlight unit (BLU). A conventional BLU using a cold cathode fluorescent lamp (CCFL) is disadvantageous in terms of mercury-induced environmental pollution, a low response rate and difficulty in partial driving. To overcome these problems, a light emitting diode (LED) has been suggested in place of the CCFL as a BLU light source. This LED-based BLU can achieve high color reproducibility, and is environment-friendly and driven by local dimming.
The BLU includes a direct-type BLU and an edge-type BLU. In the latter, a bar-shaped light source is disposed at an edge of a liquid crystal panel to irradiate light thereonto through a light guide plate. On the other hand, in the former, a surface light source using LEDs is disposed below the liquid crystal panel to directly irradiate light thereonto.
A single LED corresponds to a point light source and has a low luminous flux. Therefore, to produce a direct-type BLU for use in a big LCD-TV, typically, hundreds to thousands of LEDs are mounted on divided PCBs and then attached to a chassis structure. To enhance mechanical stability and radiation properties of the direct-type BLU, parts such as screws and gap pads are required and connectors for electrically connecting the PCBs are necessary.
FIG. 1 schematically illustrates a conventional BLU, in which FIG. 1A is a cross-sectional view and FIG. 1B is a plan view. Referring to FIG. 1, the BLU 10 includes a PCB 21 having a plurality of LEDs 25 mounted thereon, a chassis 11, and other optical sheets 33, such as a diffusion plate 31 and a prism, spaced apart from the PCB 21. A liquid crystal panel 40 is disposed above the BLU to receive white surface light emitted from the BLU 10. The PCBs 21 having the LEDs 25 mounted thereon constitute light source parts of the BLUs.
As shown in FIGS. 1A and 1B, the LEDs 25, i.e., point light sources are mounted on the divided PCBs as chips or in a package. The PCBs 21 are fixed to a bottom chassis (simply, “chassis”) 11 of a metal material disposed under the PCBs. To radiate heat emitted from the LEDs 25 smoothly, a gap pad 22 may be interposed between the chassis 11 and the PCBs 21. Engaging units such as a screw are required to fix the PCBs 21 to the chassis 11. Moreover, the divided PCBs 21 may be electrically connected to one another by connectors 23.
To manufacture the conventional BLU 10, the PCBs 21 are fixed to the chassis 11 using engaging units such as a screw. This causes an assembling process to be time-consuming and less efficient. Also, the assembling process for connecting the separate PCBs 21 to one another by connectors requires considerable resources and time. Furthermore, heat generated from the LEDs 25 is radiated outward through the PCBs 21 and the expensive gap pad 22, thereby leading to high material costs and insufficient heat radiation characteristics.